Add SSH key from variable

Also, you can use:
echo "${SSH_PRIVATE_KEY}" | ssh-add -
or
ssh-add <(echo "$SSH_PRIVATE_KEY")

ssh-add - <<< "${SSH_PRIVATE_KEY}"

If you are using Gitlab CI/CD and you want to use a variable as an SSH key you can do the following:

• Add your variable in Settings -> CI/CD -> Variables

• Use that variable in your .gitlab-ci.yml file:

  - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add - > /dev/null

Gitlab documentation